Diarrhea in patients with MTC (Medullary Thyroid Cancer) can be debilitating and, in some cases life threatening. Findings in such patients include volume depletion, renal insufficiency, and electrolyte disorders. Diarrhea can also lead to increased cost of care, reduced quality of life, and treatment delays. Not all patients benefit from conventional anti-diarrheal therapy. CASAD is proven to reduce diarrhea in humans and animals. Clays have water-binding effects, increase the absorptive capacity of the intestinal mucosa, and absorb the excess cytokines which are possible mechanisms of diarrhea in MTC. In this study, we will investigate if starting 1 g CASAD three times a day will ameliorate the severity of diarrhea in patients with MTC. Diarrhea in patients with MTC can be debilitating and, in some cases life threatening. Findings in such patients include volume depletion, renal insufficiency, and electrolyte disorders. We hypothesize that adding CASAD 3 grams/day will reduce the incidence and ameliorate the severity of diarrhea in patients with MTC.